The oligomerization of light olefins to heavier olefins is important for the production of gasoline, distillate, and feedstock for other processes. In these oligomerization processes typically C3 to C6 olefins and mixtures thereof are contacted with zeolite or solid phosphoric acid (SPA) catalyst under oligomerization conditions and converted to dimers, trimers, and other oligomers (low molecular weight polymers). The products may be useful “as is”, or they may be further processed, such as by hydrogenation or to produce functionalized products.
By way of example, a typical direct product of dimerization of C4 olefins is trimethyl pentene, useful as an octane enhancer. See, for instance, U.S. 2004/0181106 and U.S. 2004/0030212. In this regard, the presence of isobutene in the feed enhances the production of the desired highly branched product.
Isobutene in light olefin oligomerization to gasoline in Catpoly units is also useful for improved octane values. Recent work to displace solid phosphoric acid with zeolites has shown that typically zeolites are excellent catalysts for producing highly branched, high octane oligomers from isobutene containing feeds. See “EMOGAS Technology for Catpoly Units”, presented at the National Petrochemical & Refiners Association Annual Meeting, Mar. 13-15, 2005, San Francisco, Calif.; and U.S. Application No. 2004/0181106 A1.
The octenes produced by the aforementioned dimerization may instead be reacted with carbon monoxide and hydrogen in the well-known Oxo Process, to produce C9 aldehydes and/or alcohols. See, for instance, U.S. Patent Application No. 2005/0119508.
C9 aldehydes and/or alcohols have many uses and are particularly highly valued in the production of plasticizers, e.g., triisononyl phthalate. See, for instance, U.S. Pat. Nos. 3,657,150 and 6,969,736. The presence of isobutene has, in the past, presented problems in the production of plasticizers. As a result, the prior art concerning the use of zeolites to produce higher olefins for plasticizer production has in some cases focused on the presence of isobutene in the feedstock.
U.S. Patent Application Publication 2004/0006250 (WO 01-83407A1) teaches that the feedstock may comprise butenes obtained from refining or cracking and may comprise mixtures of n-butenes and isobutene having from a few wt % of isobutene up to 30 to 40 wt % isobutene at 140 to 240° C. A particular example discloses a mixed n-butene and isobutene feed to H-ZSM-57 with conditions adjusted to maintain total alkene conversion above 95%. In one example a feed comprising about 8 wt % isobutene gave a product comprising about 6.5 wt % trimethypentene with about 80 wt % octene selectivity.
C4 linear olefins are an attractive feedstock for producing octenes with zeolite catalysts because, among other reasons, the resulting octenes have triple branching of less than about 5 wt %. When isobutene is added to the oligomerization feedstock, the amount of triple-branched octenes increases to a level which is unacceptable for some end uses such as certain plasticizers.
The amount of isobutene in C4 streams typically obtained from the refinery operations (i.e., raffinate-1, or “raff-1”) is greater than the amount used in current commercial oligomerization reactions leading to Oxo Process feedstock. Thus, isobutene is removed, yielding a product, “raff-2”, useful in the Oxo Process for plasticizer-grade C9 alcohols. The isobutene removed in this step could be used in the production of, for instance, MTBE. However, with the phase out of MTBE, the usual integrated commercial process—where raff-1 was converted to raff-2 and simultaneously supplying the feed to Oxo and MTBE processes—is no longer practical.
Accordingly, for these reasons, it would be highly desirable if a process could be found to dimerize raff-1 directly, without a step of removal of all or a portion of isobutene, to yield a C8 product directly useful in the Oxo Process without removal of isobutene.
There is an extensive prior art teaching the use of zeolites for light olefin oligomerization, particularly for uni-dimensional 10-ring zeolites such as ZSM-22, ZSM-23, and SAPO-11. See, for instance, U.S. Pat. Nos. 4,962,249; 5,026,933; EP 0703888; EP 0625132; and EP 0757976. The present inventors have surprisingly discovered a process wherein multidimensional zeolites can, in embodiments, be used to oligomerize high isobutene-containing feedstocks, such as raffinate-1, to provide a product low in triple branched octenes.